Ion generator



R. LOEVINGER Feb. 28, 1950 ION GENERATOR Filed June 23, 194'? Patented Feb. 28, 1950 UNITED STATES PATENT OFFICE ION. GENERATOR Robert Loevinger, Berkeley, Calif., assignor to the United'States'of America represented by the I I United-States Atomic EnergyGommission A p icatio ;J 23, 1947, sen

"1 invention relates to ion generators, and more specifically toan ion generator particularly adapted to operate in a highly evacuated space. Prior patents granted to F. M. Penning (No. $146,025 and to W. ,Bleakney (No. 2,221,467) disclose cold cathode ion generators capable of producting ions in an evacuated space. S disclosed these patents a magnetic field acting Substantially normal to. the established electric field is utilized to elongate the electron path thereby increasing the amount of ions produced. 7 The instant invention,.in addition to embodying the principles of ion generation presented inthe above cases, furtherprovides means to expel the generated ions from the generator proper in. the form of a sharply focused beamgeven though said generator be operated in ahighly evacuated space. It is therefore an object of this invention to provide an ion generator with the'abilityto'produce an intense ion beam within a highly evacuated Space.

Another object ofthis invention is to provide'an ion generator capable of producing the center of ion concentration inapproximate coincidence with theion exit slit.

A further object of thisinvention a focused ion beam. 7

A still further object of'this invention is to proyide an ion generator capable of producing an ion beam of controlled latitudinal'dimensions.

In order to facilitate explanation and promote an understanding of the construction-andoperation of this inventionthree drawings are presented: Figure 1 being a. diagrammatic representation. of one specific mechanical configuration of the invention in planvigew; Fig. 2 being-a sectional view of Fig. L'taken along -plane-2--2; and Fig. '3 being a schematic diagram-of the associated electrical connections.

Considering Figs. 1 and 2 in detail "it-may be noted that the ion generating chamber is defined by a semicylindrical'anode 5, and two discs 6 and 1, one positioned at a distance from each open end of said anode 5, and a-flat metallic front is to produce anode 8, coveringthe concave portion of said rear anode 5, although notin electrical contact with it. This front anode 8 has a slit 9 formed therein, said slit being positioned in such a manner that its greatest dimension lies along the longitudinal axis of the semicylindrical rear anode 5. I

In addition to this front anode 8 there is provided an accelerating plate l0, disposed external to said front anode 8 and electrically insulated from it. The accelerating plate I 0 also has a scleim (c1. {SQ- 414?) s it te med th remi lseid at n ein tioned laterally and longitudinally in coinfcid nce with theslitfl .of the irontanode 8.

The mechanical featu es then may (be marized as: a .semicylindrical rear anode ii a f a ront anode '8 .pcsiticnedin proxi ty but not ,contactingsaidrear anode ihfid h a c situd nal slot 9 fo med therein: Ban a sting plate 0 situat d adjacent and pa 6. t9 the ro elec r e. a edftrom it. har ne a slit ll formed therein in alignment withtne slit 9 of the front electrode 8, and twodisc'st an one a each a d o s i .a o s' Referring now "to the electrical connections as depicted schematically in Fig. 3, aihighyoltage is impressed between the cathodes i6 and "'lland the rear anode with "the cathodesbeing ,neg a tive andthe-rear anode 5 being highly positive. The front anode 8 is maintained at a somewhat lesser positive potential than the rear anode {5. and the accelerating plate I!) =-is-maintained at approximately groundpotentialthus' being nega tiv-e with respect to the anode parts 5"and' 8.

In addition to 'the components previously described there is provided -a magnetic field, not shown, applied so as *to produce lines of force longitudinally through the rear anode 5 and I eeripendicular tothecathodes Band-I. '-I-his magnet field -may'be produced in aa -va-riety--of ways depending upon the applicationof this invention and therefore its originating agency is not depicted. T

l-Iaving now "presented the mechanical details and electrical connections of the invention :the operation "and theory will be considered. In order for an ion genera-tor to operate satisfactorily in evacuated space .a high :percentage of the ions formed must-be utilized. This 1 is due to the fact that the :pressure reduction results a decreased number of gas molecules in-a given space and thus-the number of collisions between these molecules and free electrons decreases, "thereby reducing "the number of ions formed.

Therefore in order for anion generator :to/protime an intense ion beam :whilepperatingdn :a vacuum it is necessary tomake special provisions to control the removal of a great percentage of the ions formed. In the present invention this is accomplished by two separate means operating in conjunction.

In the case of an ionization chamber defined by a cylindrical anode the center of ion concen. tration would be along the axis of said cylinder. and furthermore, as the main attractive force urging ions from said chamber must be initiated placed from the axis of said semicylinder in ,a,

direction away from said flat Wall, and yet it is equally apparent that despite said displacement,

the center of ion concentration is closer to the anode wall and thus to thesourceof the force accelerating the ions from said chamber than in,

the case of a cylindrical anode. In addition to the present mechanical configurationas herein above described a second means utilizing the force of an electric field resulting from the potential difierence between anode portions 5 and 8 is incorporated to further displace the center of ion concentration toward the ion exit slit.

The net result of the use of this configuration of the ionization chamber, and the potentials applied jority of ions are attracted by the electro fields about the accelerating plate l0,but do not impinge upon said plate due to the force of repulsion supplied by the field about the front anode 8. Therefore, the ions pass through the exit slit 9 in the front anode 8 and on through the slit l I in the accelerating plate In, emerging as a high intensity ion beam of any desired latitudinal dimension.

Althoughthe details of the invention have been discussed with reference to one specific embodiment it will be obvious to those skilled in the art "that many modifications are possible within the spirit and scope of the invention and thus the invention is not to be limited to the details shown except as defined in the following claims.

What is claimed is:

1. An ion generator comprising means for establishing a magnetic field, a tubular anode having a generally semicircular cross-section positioned in and parallel to said magnetic field,

' said tubular anode having an aperture formed to the parts defining said chamber, is to place the ,center of ion concentration extremely near the ion exit slit 9., As the ion accelerating potential is applied directly exterior to the ion exit slit 9, .a large percentage of the ions formed are forced ,through the exit slit thereby producing an intense ion beam. l

Furthermore, due to the configuration presented herein a very favorable focusing action may be produced by applying the proper biasing potential to the front anode 8. A slight variation of the front anode potentialresults in. a large variation in the latitudinal dimensions of the ion beam. Under these conditions the beam may be made very narrow, thus immeasurably increasing its value where used in conjunction with such an apparatus as a mass spectrometer.

Proceeding further with a description of the operation, it will be noted that. as a potential is applied between the cathodes Band I, and the rear anode 5, electrons are discharged from the cathodes in the direction of the anode. The action of the magnetic force upon these electrons however prevents them from coming directly in ,contact with the anode 5. Due to the interaction of the electric field and the magnet field the electrons follow a roughly helical path through the anode space until they approach sufliciently near the oppositec athode to be repelled, at which ,time they reverse direction. Thus the electron travels back and forth between the cathode 6 and l describing an approximately helical path about a magnetic line of force. As the electrons are passing back and forth in the anode space collisions occur between said electrons and any gas .-.mole'cules present in the region, and thus produce ,ions. Of these ions .formed a number impinge directly upon the cathodes-resulting in secondary electron'emission, thus adding to the number of electrons present and increasing the robability of further ion formingcollisions. However, the main the fiat wall thereof, the curved portion of the wall of said anode being electrically insulated from the remainder of said wall and at a positive potential with respect thereto, a pair of cathodes disposed adjacent the open ends of said anode and at a negative potential with respect thereto whereby an electrical discharge is produced in the region defined by said anode, and means for withdrawing'ions from said region through said aperture.

2. An ion generator comprising means for establishing a magnetic field, a tubular anode having a generally semicircular cross-section positioned in and parallel to said magnetic field, said tubular anode having an aperture formed in the fiat wall thereof, the curved portion of the wall of said anode being electrically insulated from the remainder of said wall and at a positive potential thereto, a pair of cathodes disposed adjacent the open ends of said anode and at a negative potential with respect thereto whereby an electric discharge is produced in the region defined by said anode, and means external .to said anode providing with said anode an electric field whereby ions are attracted from said region through said aperture.

3. An ion generator comprising means for establishing a magnetic field, a tubular anode having a generally semicircular cross-section positioned in and parallel to said magnetic field, said tubular anode having an aperture formed in the flat wall thereof, the curved portion'of the wall of said anode being electrically insulated from the remainder of said wall and at a positive potential with respect thereto, a pair of cathodes disposed adjacent the open ends of said anode and at a negative potential with respect thereto whereby an electric discharge is produced in the region defined by said anode, and an electrode external and adjacent the fiat wall of said anode having an aperture formed therein in alignment with said anode aperture, said electrode being at a negative potential with respect to said anode.

ROBERT LOEVINGER.

No references cited. 

